The adaptation of wireless communication devices over the past decade has brought about a sea change in the area of personal communications. Handheld wireless communication devices allow instant and nearly ubiquitous access to telephone networks and the internet.
Looking to the future, there is an interest in enabling handheld wireless communication devices to handle higher bandwidth communication. Among other things, this would facilitate sending and receiving of video, music, and performing other high speed file transfer via handheld wireless communication devices. However, any such plans must work within the bandwidth constraints imposed by government regulations. In order to maximize the effective data bandwidth of a given frequency band, researchers have developed a new class of physical layer communication techniques known as Multi-Input Multi-Output (MIMO). MIMO methods use multiple antennas having different radiation patterns, but operated in the same frequency band to establish, at least partially, independent channels. Thus, using the same frequency band, enhanced bandwidth, or enhanced data reliability can be obtained. The enhancements afforded by MIMO methods depend on the degree of decorrelation between signals transmitted from or received by multiple antennas. In endeavoring to apply MIMO methods to handheld devices one faces limitations imposed by constraints on the practical external design of handheld devices (having multiple antennas protruding in different directions is undesirable), the limited size of handheld devices, and in particular the limited size of the ground structures (e.g., Printed Circuit Board (PCB) ground planes) of handheld devices which serve as ground references or counterpoises for antennas of handheld devices. The foregoing limitations tend to constrain the achievable decorrelation (increase the correlation) between signals associated with multiple antennas, and thereby limit the enhancement that MIMO methods can yield. What is needed is a handheld device design that meets foregoing limitations but can effectively utilize MIMO.
Another goal in designing handheld wireless communication devices, especially for certain market segments, is cost reduction. Handheld wireless devices typically include a transmit/receive switch network which allows a single antenna to be used for both receiving and transmitting signals. At present the high cost of transmit/receive switch networks presents an impediment to further reduction of the costs of handheld wireless communication devices.